Love bites on the neck of the young female Tas­manian devil in my lap tell me she has recently had a sexual encounter. They also indicate something ominous: she might well be dead before she can raise her first litter of pups.

I (Jones) am sitting on the ground holding a devil that I trapped in Freycinet National Park on the eastern coast of Tasmania—a wild jewel of an island to the south of the mainland of Australia. It was here, in 2001, that I first witnessed a hideous disease that causes large, festering tumors on the face of these marsupials, impairing feeding and routinely killing them within six months of infection. Today the Freycinet population has almost disappeared—a reflection of what is happening across most of the animal’s range. First detected in 1996, up in the northeastern corner of the island, the cancer—now known to be contagious—has reduced devil populations across Tasmania by up to 95 percent, pushing the species, which lives only on this island, to the edge of extinction.